Note pubs.acs.org/joc
Iridium-Catalyzed Alkylation of Methylquinolines with Alcohols Yasushi Obora,* Shinji Ogawa, and Nobuyuki Yamamoto Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita, Osaka 564-8680, Japan S Supporting Information *
ABSTRACT: Iridium-catalyzed alkylation of methylquinolines at the methyl substituent was achieved using alcohols as alkylating agents. The reaction proceeded through a transfer hydrogenation pathway from the alcohol to the Ir complex, affording an aldehyde and Ir−H species, followed by baseassisted aldol condensation and hydrogenation. This method provides an atom-economical and convenient route to alkylquinolines from easily accessible methylquinolines.
Q
ligands such as py2NP(iPr)2.11 Reflecting on these related studies, we realized the importance of the necessity of investigating efficient synthetic methods for obtaining alkylquinolines from easily accessible methylquinolines using simple catalytic systems. Here we report a simple and versatile method for the preparation of various alkylquinolines from methylquinolines and alcohols in the presence of an [Ir(OH)(cod)]2 catalyst combined with a PPh3 ligand and a base. To determine the optimum reaction conditions, the reaction of 2-methylquinoline (1a) with benzyl alcohol (2a) was chosen as a model reaction and carried out under various reaction conditions. The results for the alkylation reactions are shown in Table 1. For example, the reaction of 1a (3 mmol) with 2a (1 mmol) was performed in the presence of [Ir(OH)(cod)]2 (0.05 mmol, 5 mol %) combined with PPh3 (0.20 mmol, 20 mol %) and t-BuOK (0.5 mmol, 50 mol %) in 1,4-dioxane (1 mL) at 130 °C for 24 h, giving 3a in quantitative yield (Table 1, entry 1). With regard to the Ir complex, [Ir(OMe)(cod)]2, [IrCl(cod)]2, and [Cp*IrCl2]2 gave comparable good yields (Table 1, entries 2−4). However, when IrCl3·3H2O and an Rh analogue, [RhCl(cod)]2, were used, the reactions were sluggish (Table 1, entries 5 and 6). As the base added in the reaction, tBuOK gave the best result, and strong bases such as KOH gave the product in good yield, but weak bases such as Na2CO3 resulted in total inactivity under these conditions (Table 1, entries 1, 7, and 8). It was found that the addition of a phosphine ligand was necessary to obtain higher yields from the reaction; the reaction was sluggish if a diphosphine was used, or if the reaction was performed in the absence of a phosphine ligand (Table 1, entries 9−12). In this reaction, high yield formation of 3a was achieved by using excess (3 equiv to 2a) amount of 1a (Table 1, entry 1). However, the conversion of 1a was 35% and most of unreacted 1a was recovered (59%) by distillation after the reaction. On the other hand, the equimolar reaction of 1a with 2a resulted in decrease in the yield of 3a (Table 1, entry 13) because 1a possesses a less acidic methyl
uinolines and their derivatives are important motifs in pharmaceutical and agricultural chemistry and are used as building blocks in total syntheses of natural products.1 Various methods for synthesizing quinolines and quinolinebased natural products have therefore been developed.2 In particular, the introduction of alkyl-chain moieties into benzoquinones is an important chemical transformation.3 Conventionally, methylquinolines have been chosen as the starting materials for the preparation of alkylated quinoline derivatives because they are easily accessible.3 The reaction of a methylquinoline with n-BuLi followed by reaction with an alkyl halide is the classic method of synthesizing alkylquinolines.3 However, since a prerequisite of the conventional reaction is the use of aryl halides as substrates, this method suffers from formation of undesired stoichiometric amounts of waste salts generated from alkyl halides and bases. The development of an improved reaction that is environmentally benign and uses easily accessible starting materials for the introduction of alkyl groups on methylquinolines is therefore highly desirable. It is well-known that Ir and Ru complexes serve as efficient catalysts for transfer hydrogenation (also known as hydrogen borrowing) from alcohols to aldehydes and ketones.4 Much research has focused on both α-alkylation and β-alkylation reactions using alcohols as alkylating agents.5 Our group has focused on Ir-catalyzed α-alkylations of methyl ketones, methyl esters, and active methylene compounds, and Guerbet-type dimerizations of alcohols.6 We achieved Ir-catalyzed alcohol transformations to esters,7 and reactions of alcohols with alkynes or enones led to homoallylic alcohols,8 enones,9 and 1,3-diketones.10 During the course of our investigations, we became aware of the development of methyl alkylation of methylquinolines by a transfer hydrogenation method using alcohols as alkylating agents. This is a convenient method for obtaining synthetically useful quinoline derivatives and also for achieving high-yield direct alkylation of less acidic methyl substituents on the aromatic compound using a simple Ir catalyst system. Recently, Kempe and co-workers reported the alkylations of methylpyrimidines and picolines using Ir complexes bearing P,N-type © XXXX American Chemical Society
Received: September 6, 2012
A
dx.doi.org/10.1021/jo3019347 | J. Org. Chem. XXXX, XXX, XXX−XXX
The Journal of Organic Chemistry
Note
Table 1. Ir-Catalyzed Reactions of 2-Methylquinoline (1a) with Benzyl Alcohol (2a) under Various Conditionsa
entry
Ir catalyst
base
ligand
yield 3a (%)b
1 2 3 4 5 6 7 8 9 10 11e 12 13f
[Ir(OH)(cod)]2 [Ir(OMe)(cod)]2 [IrCl(cod)]2 [Cp*IrCl2]2 IrCl3·3H2O [RhCl(cod)]2 [Ir(OH)(cod)]2 [Ir(OH)(cod)]2 [Ir(OH)(cod)]2 [Ir(OH)(cod)]2 [Ir(OH)(cod)]2 [Ir(OH)(cod)]2 [Ir(OH)(cod)]2
t-BuOK t-BuOK t-BuOK t-BuOK t-BuOK t-BuOK KOH Na2CO3 t-BuOK t-BuOK t-BuOK t-BuOK t-BuOK
PPh3 PPh3 PPh3 PPh3 PPh3 PPh3 PPh3 PPh3 PCy3 P(n-Oct)3 dppp None PPh3
quant (92) 86 81 64 1c 7 58 n.d.d 59 40 12 10 41g
Table 2. Ir-Catalyzed Reactions of 2-Methylquinoline (1a) with Primary Alcohols 2a
a Conditions: 1a (3 mmol) was allowed to react with 2a (1 mmol) in the presence of Ir catalyst (0.05 mmol), ligand (0.20 mmol), and base (0.50 mmol) in 1,4-dioxane (1 mL) at 130 °C for 24 h. bGC yields based on 2a except the value in the parentheses. c28% of 2stylquinoline was observed. dNot detected by GC. edppp (0.10 mmol) was used. f2-Methylquinoline (1 mmol) was used. gConversions of 1a and 2a were 14% and 46%.
group and shows low reactivity in the reaction. No reaction took place in the absence of an Ir complex. 1,4-Dioxane is the most suitable solvent for the reactions (Table 1, entry 1). The use of other selected solvents under these conditions gave the following results: p-xylene (43%), diglyme (85%), 1,2-dichlorobenzene (34%), and octane (50%). The methyl alkylation of 2-methylquinoline proceeded smoothly using various substituted benzyl alcohols bearing electron-donating/-withdrawing groups (Table 2, entries 1−7), as well as using aliphatic alcohols (Table 2, entries 8−11), giving the corresponding products (3b−3l) in good to excellent yields under the same condition as for entry 1 in Table 1; the results are shown in Table 2. Although this reaction tolerated various primary alcohols as alkylating agents, unfortunately, the use of secondary alcohols such as benzhydrol was sluggish under these conditions. The present catalytic system was successfully extended to reactions of various heteroaromatic compounds, and the results are shown in Table 3. 4-Methylquinoline gave the corresponding product in good yield (Table 3, entry 1), but 3- and 6methylquinoline were totally inactive (Table 3, entries 2 and 3). The use of 2-methylquinoxaline and 2-methylbenzoxazole gave the desired methyl-alkylated products (3n and 3o) in high to excellent yields (Table 3, entries 4 and 5). In contrast, the use of 2-methylpyridine gave the corresponding alkylated pyridine (3p) in only 21% yield (Table 3, entry 6). These results suggest that the use of methylquinolines with benzo substituents on the methylpyridine scaffold is a prerequisite for the reaction to proceed efficiently and in good yield. Furthermore, the use of 2- or 4-methylquinoline efficiently increases the acidity of the methyl protons for the deprotonation step on addition of a base in the catalytic system (pK a values are 25 for 2-methylquinoline, 25 for 4-
a Conditions: 1a (3 mmol) was allowed to react with 2 (1 mmol) in the presence of Ir catalyst (0.05 mmol), ligand (0.20 mmol), and base (0.50 mmol) in 1,4-dioxane (1 mL) at 130 °C for 24 h. bt-BuOK (0.70 mmol) was used. c2-Methylquinoline (10 mmol) was used.
methylquinoline, 32 for 3-methylquinoline, and 29.5 for 2methylpyridine).12 A similar enhancement of the reaction by a benzo-substituent effect was observed in our study of Ir-catalyzed reactions of 1naphthylamine and diols, giving benzo[h]quinolines and benzoindoles.13 To obtain further insights into the present reaction, the time course of the reaction of 1a and 2a was monitored (Figure 1). In the early stage of the reaction, the formation of 2B
dx.doi.org/10.1021/jo3019347 | J. Org. Chem. XXXX, XXX, XXX−XXX
The Journal of Organic Chemistry
Note
The above alkylation reaction is therefore thought to proceed through the following sequential reactions, involving three key steps, as proposed in previous reviews (Figure 2):4 (i) hydrogen transfer from alcohol 2 to an Ir complex, giving aldehyde A and an Ir hydride intermediate B; (ii) basecatalyzed aldol condensation by a coupling reaction of A and 1a to form alkenylquinoline 4;1c,14 and (iii) selective hydrogenation of 4 by the Ir hydride complex generated during the course of the reaction, leading to alkylated quinoline 3. In conclusion, an efficient and selective alkylation of methylquinolines was successfully developed using an Ir complex combined with a phosphine ligand and a base. The reaction provides a simple and atom-economical direct route to alkylquinolines, as the exclusive products, in good to excellent yields.
Table 3. Ir-Catalyzed Reactions of Heteroaromatic Compounds 1 with Benzyl Alcohol (2a)a
■
EXPERIMENTAL SECTION
General. GC analysis was performed with a flame ionization detector using a 0.22 mm × 25 m capillary column (BP-5). 1H and 13C NMR were measured at 400 and 100 MHz, respectively, in CDCl3 with Me4Si as the internal standard. The products were characterized by 1H NMR, 13C NMR, and GC−MS. The yields of products were estimated from the peak areas based on the internal standard technique using GC. Compounds 3a,15a 3b,15b 3c,15c 3e,15d 3i,15e 3j,15e 3k,15e 3m,15f 3n,15g 3o,15h 3p,15i and 4a1c were reported previously. Typical Reaction (Table 1, entry 1). A mixture of [Ir(OH)(cod)]2 (32 mg, 0.05 mmol), PPh3 (52 mg, 0.20 mmol), t-BuOK (56 mg, 0.5 mmol), 1a (0.43 g, 3 mmol), and 2a (0.1 g, 1 mmol) in 1,4dioxane (1 mL) was stirred at 130 °C for 24 h under Ar. The conversions and yields of products were estimated from peak areas based on an internal standard using GC, and the product 3a was obtained in quantitative yield. The product 3a was isolated by column chromatography (230−400 mesh silica gel, n-hexane/ethyl acetate = 10/1) and Kugelrohr distillation (100 °C (pot)/0.3 mmHg, 1 h) in 92% yield (215 mg) as yellow liquid. After the reaction, unreacted 1a (1.77 mmol, 253 mg, 59%) was recovered by Kugelrohr distillation (95 °C (pot)/0.3 mmHg, 1 h). Compound 3b. Yield 88% (232 mg), yellow solid, mp 56−57 °C (lit.15b mp 58−59 °C) Compound 3m. Yield 56% (131 mg), yellow solid, mp 99−100 °C (lit.15f mp 96−97 °C) Compound 3o. Yield 72% (161 mg), white solid, mp 53−54 °C (lit.15h mp 53−54 °C) Compound 3d. Yield 76% (188 mg), yellow liquid; 1H NMR δ 8.09−7.00 (m, 10H), 3.29−3.25 (m, 2H), 3.13−3.09 (m, 2H), 2.312 (s, 3H); 13C NMR δ 161.9 (C), 148.0 (C), 139.7 (C), 136.2 (CH), 136.0 (C), 130.2 (CH), 129.4 (CH), 128.9 (CH), 128.8 (CH), 127.5 (CH), 126.8 (C), 126.1 (CH), 126.0 (CH), 125.8 (CH), 121.5 (CH), 39.7 (CH2), 33.2 (CH2), 19.3 (CH3); IR (neat, cm−1) 3053, 2920, 1599, 1504, 1427, 827, 785, 745; GC−MS (EI) m/z (relative intensity) 247 (89) [M]+, 246 (100), 156 (56), 142 (2), 128 (14), 105 (11), 91 (3), 77(14); HRMS (EI-TOF) m/z calcd for C18H17N [M]+ 247.1361, found 247.1357. Compound 3f. Yield 89% (258 mg), yellow solid, mp 66−67 °C; 1 H NMR δ 8.09−7.20 (m, 10H), 3.31−3.27 (m, 2H), 3.14−3.10 (m, 2H), 1.31 (s, 9H); 13C NMR δ 162.0 (C), 148.8 (C), 148.0 (C), 138.5 (C), 136.2 (CH), 129.3 (CH), 128.9 (CH), 128.1 (CH), 127.5 (CH), 126.8 (C), 125.7 (CH), 125.3 (CH), 121.5 (CH), 41.0 (CH2), 35.4 (CH2), 34.4 (C), 31.4 (CH3); IR (neat, cm−1) 2959, 1599, 1500, 1425, 827, 752; GC−MS (EI) m/z (relative intensity) 289 (94) [M]+, 288 (100), 274 (27), 258 (2), 244 (1), 232 (15), 156 (34), 147 (8), 142 (4), 132 (6), 128 (11), 119 (3), 118 (2), 117 (18), 105 (5), 104 (2), 103 (3), 91 (10), 89 (3), 77 (4), 57 (3); HRMS (EI-TOF) m/z calcd for C21H23N [M]+ 289.1830, found 289.1840. Compound 3g. Yield 82% (232 mg), yellow solid, mp 125−126 °C; 1H NMR δ 8.10−7.17 (m, 13H), 3.39−3.28 (m, 4H), 3.13−3.09 (m, 2H); 13C NMR δ 161.7 (C), 148.0 (C), 139.0 (C), 136.2 (CH),
a Conditions: 1 (3 mmol) was allowed to react 2a with (1 mmol) in the presence of Ir catalyst (0.05 mmol), ligand (0.20 mmol), and base (0.50 mmol) in 1,4-dioxane (1 mL) at 130 °C for 24 h. bt-BuOK (0.70 mmol) was used. c1 (5 mmol) was used. dNot detected by GC. etBuOK (1 mmol) was used.
Figure 1. Time-course monitoring of reaction of 1a with 2a.
phenylethenylquinoline (4a) was detected, which showed that 4a was an intermediate in the reaction. We interrupted the reaction course at 1 h, and the conversions of 1a and 2a were 10% and 41%, respectively. Products 3a and 4a were isolated during the course of the reaction. The results, shown in Figure 1 and Scheme 1, clearly indicate that 4a was an intermediate in the reaction. C
dx.doi.org/10.1021/jo3019347 | J. Org. Chem. XXXX, XXX, XXX−XXX
The Journal of Organic Chemistry
Note
Scheme 1. Observed Reaction Intermediate 4a in the Reaction of 1a with 2a
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by the MEXT-Supported Program for the Strategic Research Foundation at Private Universities (2010-2014), ALCA from Japan Science and Technology Agency (JST), and the Kansai University Research Grants: Grant-in Aid for Encouragement of Scientists, 2012.
■
(1) (a) Sundbelg, R. J. In Kirk-Othmer Encyclopedia of Chemical Technology; Kroschwitz, J. I, Howe-Grand, M., Eds.; Wiley: New York, 1995; Vol. 14, p 161. (b) Katritzky, A. R.; Rachwal, S.; Rachwal, B. Tetrahedron 1996, 52, 15031. (c) Wang, T.; Zhuo, L.-G.; Li, Z.; Chen, F.; Ding, Z.; He, Y.; Fan, Q.-H.; Xiang, J.; Yu, Z.-X.; Chan, A. S. C. J. Am. Chem. Soc. 2011, 133, 9878 and references therein. (2) (a) Robinson, B. Chem. Rev. 1963, 63, 373. (b) Augustine, R. L.; Gustavesen, A. J.; Wanat, S. F.; Pattison, I. C.; Houghton, K. S.; Koleter, G. J. Org. Chem. 1973, 38, 3004. (c) Rano, T. A.; McMaster, E. S.; Pelton, P. D.; Yang, M.; Demarest, K. T.; Kuo, G. H. Bioorg. Med. Chem. Lett. 2009, 19, 2456. (d) Nallan, L.; Bauer, K. D.; Bendale, P.; Rivas, K.; Yokoyama, K.; Hoenéy, C. P.; Pendyala, P. R.; Floyd, D.; Lombardo, L. J.; Williams, D. K.; Hamilton, A.; Sebti, S.; Windsor, W. T.; Weber, P. C.; Buckner, F. S.; Chakrabarti, D.; Gelb, M. H.; Van Voorhis, W. C. J. Med. Chem. 2005, 48, 1263 and references therein. (3) (a) Robert, V. S.; Jimmy, W. C. J. Org. Chem. 1990, 55, 2237. (b) Vimal, P.; James, A. R.; Martin, W. Tetrahedron: Asymmetry 2010, 21, 1549. (4) For selected reviews, see: (a) Ourida, S.; Williams, J. M. J. Top. Organomet. Chem. 2011, 34, 77. (b) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. J. Am. Chem. Soc. 2005, 127, 10840. (c) Hanasaka, F.; Fujita, K.; Yamaguchi, R. Organometallics 2004, 23, 1490. (d) Hamid, M. H. S. A.; Slatford, P. A; Williams, J. M. J. Adv. Synth. Catal. 2007, 349, 1555. (e) Bower, J. F.; Kim, I. S.; Patman, R. L.; Krische, M. J. Angew. Chem., Int. Ed. 2009, 48, 34. (f) Guillena, G.; Ramon, D. J.; Yus, M. Chem. Rev. 2010, 110, 1611. (g) Debereiner, G. E.; Crabtree, R. H. Chem. Rev. 2010, 110, 681. (h) Takeuchi, R.; Kezuka, S. Synthesis 2006, 3349. (5) For selected examples, see: (a) Cho, C. S.; Kim, B. T.; Kim, T.-J.; Shim, S. C. J. Org. Chem. 2001, 66, 9020. (b) Ndou, A. S.; Plint, N.; Coville, N. J. Appl. Catal. A: Gen. 2003, 251, 337. (c) Cho, C. S.; Kim, B. T.; Kim, H.-S.; Kim, T.-J.; Shim, S. C. Organometallics 2003, 22, 3608. (d) Martínez, R.; Ramón, D. J.; Yus, M. Tetrahedron 2006, 62, 8982. (e) Fujita, K.; Asai, C.; Yamaguchi, T.; Hanasaka, F.; Yamaguchi, R. Org. Lett. 2005, 7, 4017. (f) Onodera, G.; Nishibayashi, Y.; Uemura, S. Angew. Chem., Int. Ed. 2006, 45, 3819. (g) Guillena, G.; Ramon, D. J.; Yus, M. Angew. Chem., Int. Ed. 2007, 46, 2358. (h) Nixon, T. D.; Whittlesey, M. K.; Williams, J. M. J. Dalton Trans. 2009, 753 and references therein. (6) (a) Taniguchi, K.; Nakagawa, H.; Hirabayashi, T.; Sakaguchi, S.; Ishii, Y. J. Am. Chem. Soc. 2004, 126, 72. (b) Maeda, K.; Obora, Y.; Sakaguchi, S.; Ishii, Y. Bull. Chem. Soc. Jpn. 2008, 81, 689. (c) Iuchi, Y.; Obora, Y.; Ishii, Y. J. Am. Chem. Soc. 2010, 132, 2536. (d) Morita, M.; Obora, Y.; Ishii, Y. Chem. Commun. 2007, 2850. (e) Obora, Y.; Anno, Y.; Okamoto, R.; Matsu-ura, T.; Ishii, Y. Angew. Chem., lnd. Ed. 2011, 50, 8618. (f) Matsu-ura, T.; Sakaguchi, S.; Obora, Y.; Ishii, Y. J. Org. Chem. 2006, 71, 8306.
Figure 2. Plausible reaction pathway. 133.6 (C), 132.0 (C), 129.4 (CH), 128.9 (CH), 127.9 (CH), 127.6 (CH), 127.5 (CH), 127.5 (CH), 127.3 (CH), 126.8 (C), 126.6 (CH), 125.9 (CH), 125.8 (CH), 125.2 (CH), 121.6 (CH), 40.9 (CH2), 36.0 (CH2); IR (neat, cm−1) 2916, 1597, 1501, 1425, 1126, 858, 829, 746; GC−MS (EI) m/z (relative intensity) 283 (88) [M]+, 282 (100), 156 (35), 155 (4), 142 (9), 141 (44), 128 (17), 127 (4). Anal. Calcd for C21H17N: C, 89.01; H, 6.05; N, 4.94. Found: C, 89.01; H, 5.97; N, 4.93. Compound 3h. Yield 36% (96 mg), yellow solid, mp 56−57 °C; 1 H NMR δ 8.07−7.12 (m, 10H), 3.26−3.22 (m, 2H), 3.14−3.10 (m, 2H); 13C NMR δ 161.2 (C), 147.9 (C), 139.9 (C), 136.2 (CH), 131.6 (C), 129.8 (CH), 129.4 (CH), 128.8 (CH), 128.4 (CH), 127.5 (CH), 126.7 (C), 125.8 (CH), 121.4 (CH), 40.6 (CH2), 35.0 (CH2); IR (neat, cm−1) 3057, 2924, 1600, 1501, 1427, 1090, 1013, 827, 762; GC−MS (EI) m/z (relative intensity) 267 (89) [M]+, 266 (100), 232 (7), 156 (70), 142 (4), 128 (22), 125 (19), 91(1), 77(9); HRMS (EITOF) m/z calcd for C17H14NCl [M]+ 267.0815, found 267.0820. Compound 3l. Yield 78% (199 mg), yellow liquid; 1H NMR δ 7.98−7.18 (m, 6H), 2.90−2.86 (m, 2H), 1.70−1.67 (m, 2H), 1.33− 1.21 (m, 9H), 0.83−0.80 (t, J = 7.2 Hz 3H), 0.83−0.79 (t, J = 7.2, Hz 3H); 13C NMR δ 163.47 (C), 147.9 (C), 136.1 (CH), 129.2 (CH), 128.8 (CH), 127.4 (CH), 126.7 (C), 125.6 (C), 121.3 (CH), 38.9 (CH), 36.8 (CH2), 33.5 (CH2), 32.7 (CH2), 28.9 (CH2), 25.7 (CH2), 23.1 (CH2), 14.1 (CH3), 10.8 (CH3); IR (neat, cm−1) 2956, 2926, 2859, 1601, 1504, 1458, 1425, 826, 752; GC−MS (EI) m/z (relative intensity) 255 (1) [M]+, 226 (6), 198 (5), 184 (2), 170 (1), 156 (39), 143 (100), 142 (4), 128 (6), 57 (2), 43 (2), 29 (4); HRMS (EI-TOF) m/z calcd for C18H25N [M]+ 255.1987, found 255.1993.
■
ASSOCIATED CONTENT
S Supporting Information *
1
H, and 13C NMR spectra for products. This material is available free of charge via the Internet at http://pubs.acs.org.
■
REFERENCES
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. D
dx.doi.org/10.1021/jo3019347 | J. Org. Chem. XXXX, XXX, XXX−XXX
The Journal of Organic Chemistry
Note
(7) (a) Izumi, A.; Obora, Y.; Sakaguchi, S.; Ishii, Y. Tetrahedron Lett. 2006, 47, 9199. (b) Yamamoto, N.; Obora, Y.; Ishii, Y. Chem. Lett. 2009, 38, 1106. (c) Yamamoto, N.; Obora, Y.; Ishii, Y. J. Org. Chem. 2011, 76, 2937. (8) Obora, Y.; Hatanaka, S.; Ishii, Y. Org. Lett. 2009, 11, 3510. (9) Hatanaka, S.; Obora, Y.; Ishii, Y. Chem.Eur. J. 2010, 16, 1883. (10) Obora, Y.; Nakamura, K.; Hatanaka, S. Chem. Commun. 2012, 48, 6720. (11) Blank, B.; Kempe, R. J. Am. Chem. Soc. 2010, 132, 924. (12) (a) Batterham, T. J.; Brown, D. J.; Paddon-Row, M. N. J. Chem. Soc. B 1967, 171. (b) Fischer, A.; Morgan, M. W.; Eaborn, C. J. Organomet. Chem. 1977, 136, 323. (13) Aramoto, H.; Obora, Y.; Ishii, Y. J. Org. Chem. 2009, 74, 628. (14) Schierlein, W. K.; Prelog, V. Helv. Chim. Acta 1957, 24, 205. (15) (a) Ramesh, C; Kavala, V; Kuo, C, W.; Yao, C, F. Tetrahedron Lett. 2010, 51, 5234. (b) Bergstrom, F. W.; Norton, T. R.; Seibert, R. A. J. Org. Chem. 1945, 10, 452. (c) Lautens, M.; Roy, A.; Fukuoka, K.; Fagnou, K.; Martin, M. B. J. Am. Chem. Soc. 2001, 123, 5358. (d) Rueping, M.; Koenigs, R. M. Chem Commun. 2011, 47, 304. (e) Fakhfakh, M. A.; Franck, X.; Fournet, A.; Hocquemiller, R.; Figadère, B. Tetrahedron Lett. 2001, 42, 3847. (f) Ogiwara, Y.; Kochi, T.; Kakiuchi, F. Org. Lett. 2011, 13, 3254. (g) Martin, L. J.; Marzinzik, A. L.; Ley, S. V.; Baxendale, I. R. Org. Lett. 2011, 13, 320. (h) Terashima, M.; Ishii, M.; Kanaoka, Y. Synthesis 1982, 484. (i) Azzena, U.; Pisano, L.; Antonello, S.; Maran, F. J. Org. Chem. 2009, 74, 8064.
E
dx.doi.org/10.1021/jo3019347 | J. Org. Chem. XXXX, XXX, XXX−XXX
